The invention is in the field of devices of the type installed in residential load centers to protect electrical branch circuits from damage due to overcurrents and transients. A contemporary residential load center of this type is commercially available, for example under Siemens ENERGY AND AUTOMATION, INC. Catalog Number G2040MB1200CU or G1224MB1100CU, and has openings for push-on circuit breakers each serving to electrically connect a line stab to a load under normal operating conditions but to electrically disconnect the line from the load in case of overcurrent. An exemplary circuit breaker of this type is commercially available under Siemens ENERGY AND AUTOMATION, INC. Catalog Number Q21515. Exemplary features of a circuit breaker are described in U.S. Pat. No. 4,479,101. One circuit breaker of this type is 1/2 inch wide per line, so that a circuit breaker for two lines occupies an inch-wide push-in opening in the load center. Surge arrestors or suppressors or protectors also can be installed in a load center to provide protection against surges such as due to lightning. Examples of devices of this general type are discussed in U.S. Pat. Nos. 2,839,635, 3,152,287, 3,312,889, 3,464,040, 3,717,792, 3,733,516, 3,737,725, 3,887,849, 3,889,222, 3,934,175, 3,947,726, 4,019,097, 4,023,071, 4,068,277, 4,068,281, 4,084,207 and 4,168,514. It is believed that known surge suppressors suffer from shortcomings such as requiring additional wire connectors or special circuit features for proper circuit installation, providing protection only or mainly for surges with low energy levels, being prone to failure, using for protection only a circuit element such as a Metal Oxide Varistor (MOV) that could fail catastrophically if faulted, requiring long connecting electrical leads which could cause high circuit inductance and resulting high transient voltage discharge levels, requiring excessive use of non-standard components or manufacturing techniques, and/or having no means for conveniently showing operational status. The latest of these patents appears to propose a combined device incorporating both a circuit breaker and a surge arrestor in a single package, and is said to overcome certain shortcomings of the prior art. However, the patent states that the arrestor's varistor is packaged in a thermally coupled relationship with the circuit breaker's thermal element, typically a bi-metal, such that the heat generated by the flow of abnormal leakage current through the varistor will also indirectly heat the thermal element, thus contributing to the thermal tripping of the circuit breaker. See column 2, lines 26-43 and column 6, lines 13-29 in the cited patent. In addition, the cited patent does not appear to propose a means for readily and conveniently ascertaining the operational status of the lightning arrestor.
It is believed in view of the foregoing that a need remains for a circuit breaker/surge arrestor package that could be efficiently manufactured using only or mainly standard components and manufacturing techniques, could be easily and conveniently installed in a contemporary load center, and could provide effective protection as well as an easily ascertainable indication of operational status. The invention is directed to meeting such a need and, in a nonlimiting example, is embodied in a circuit breaker/surge arrestor comprising a circuit breaker which can be plugged into a load center to connect a line to a load and has a thermal trip circuit and a magnetic trip circuit each responsive to an overcurrent having respective characteristics to trip the circuit breaker and thereby disconnect the load from the line, a surge arrestor in series with the circuit breaker comprising a Metal Oxide Varistor (MOV) responsive to an onset of a respective threshold of current passage through the MOV to cause the circuit breaker's magnetic trip circuit to trip before the thermal trip circuit has had an opportunity to trip, and an indicator circuit coupled with the surge arrestor and comprising an indicator light which is visible from outside the surge arrestor and has ON and OFF states indicative of the operational status of the MOV and the circuit breaker. The exemplary circuit breaker in accordance with the invention can be manufactured using a standard circuit breaker, which can be used alone as a circuit breaker only but becomes a part of a package incorporating the invention when integrated with a surge arrestor in accordance with the invention. The normal housing of a standard circuit breaker can become at least a part of a thermal barrier between the MOV in the arrestor and the thermal trip circuit in the breaker. In the circuit breaker/surge arrestor in accordance with the invention, the response characteristics of the breaker and the arrestor matched with each other such that the breaker would trip magnetically in response to a certain threshold a substantially continuous current through the arrestor but not for example in response to an impulse that might momentarily be at the same or even a somewhat higher level but is too short in duration to present a danger.